In a conventional illumination apparatus, it is sometimes the case that the light is not uniformly projected from a light projecting surface, thereby generating illuminance unevenness or color unevenness which leads to a failure to make the illuminance of an irradiated surface uniform. Various kinds of devices and methods are used in an effort to reduce the illuminance unevenness.
For example, there is known a method of reducing illuminance unevenness or color unevenness on an irradiated surface by providing dimple-shaped concave portions 7a on a light projecting surface of an optical member of an illumination apparatus as shown in FIG. 7A. The concave portions 7a are of a regular hexagonal shape and are arranged in a honeycomb structure with no clearance left therebetween. Using the honeycomb structure, light dimming regions differing in transmittance are formed so that the light beams can interfere with one another. The illuminance unevenness on an irradiated surface is reduced while maintaining the transmittance of the light beams.
In order to reduce generation of illuminance unevenness in an illumination apparatus, there is disclosed an illumination apparatus including a molded body for a light source cover which is resistant to resin degradation and capable of realizing a light-irradiated surface with reduced brightness unevenness and enhanced brightness uniformity (see, e.g., Japanese Patent Application Patent No. 2009-76343).
However, even if the illumination apparatus employs the conventional optical member 7 in which the concave portions 7a are arranged on the light projecting surface in a honeycomb structure, a problem is posed in that illuminance unevenness is generated on the irradiated surface 8 as illustrated in FIG. 7B.